[Distribution of CH4 in the suburb of Changsha City, China]

To study the variation of atmospheric CH4 concentration in the Yangtze River region, air samples which collected weekly using flasks from the suburb of Changsha City from 2007 to 2011 and the CH4 concentration was measured by gas chromatography. CH4 concentrations were analyzed combined with ground meteorological elements and backward trajectories to explore the CH4 concentration variations with source-sink relationships. The results showed that during the observation period, the annual mean concentration of CH4 was in the range 2012 x 10(-9) - 2075 x 10(-9) (volume mixing ratio, the same below). The difference between the maximum and minimum monthly mean of CH4 concentrations was 152 x 10(-9), with the highest concentration observed in autumn and the lowest in spring. Analysis of the surface wind showed that the concentration of CH4 was controlled by northwest wind and southerly winds alternately, and the contribution rate was 41.1% and 20.4%, respectively. Surface winds causing CH4 concentration uplift included W-WNW-NW in all four seasons, ESE-SE in summer and S in winter; while S in spring and summer have resulted in the decrease of CH4 concentration. Analysis of the air mass transport showed that the concentration of CH4 in the suburb of Changsha was significantly contributed by air masses from rice-producing areas in summer and high energy consumption areas in winter, and was cleared by air masses of long-distance transport from southern district.